The present invention relates to a flow rate measurement apparatus for measuring a flow rate of fluid, such as gas or the like.
There are many known methods for measuring the flow rate of fluids, such as gases, liquids, etc. Especially, reliable flow velocity/flow rate measurement apparatuses which utilize ultrasonic waves have been remarkably developed thanks to progress in techniques of electronics. The flow velocity/flow rate measurement apparatuses which utilize ultrasonic waves can be employed in various application fields, such as a meter for fuel gas, an industrial measurement device, a blood-flow meter for medical use, measurement of flow velocity in the ocean or atmosphere, etc. Such flow velocity/flow rate measurement apparatuses can directly utilize ultrasonic waves in some cases, and in other cases, can be utilized as a detecting section of a measurement apparatus which operates based on other measurement principles and which indirectly utilize ultrasonic waves.
As shown in FIG. 21, a conventional ultrasonic flow-velocity meter includes: an ultrasonic transmitting transducer 2 which is placed in a measurement path 1 through which fluid flows; a transmission circuit 3 for driving the ultrasonic transmitting transducer 2; a controller 5 for simultaneously transmitting a vibration start signal from the transmission circuit 3 and for starting a timer 4; an ultrasonic receiving transducer 6 which is placed upstream or downstream of the ultrasonic transducer 2 and which receives ultrasonic waves emitted by the ultrasonic transducer 2; an amplifier 7 for amplifying a received signal from the ultrasonic receiving transducer 6; and a comparator 9 for comparing the signal output from the amplifier 7 and a reference signal output from a reference signal generating section 8 and for stopping the timer 4 when the relationship of the magnitudes between these signals is inverted. This conventional ultrasonic flow-velocity meter is structured such that the flow velocity of the measured fluid is measured based on a time measured by the timer 4.
In the above ultrasonic flow-velocity meter, in response to a start signal from the controller 5, the transmission circuit 3 outputs a pulse during a predetermined time so as to drive the ultrasonic transducer 2. An ultrasonic wave emitted by the ultrasonic transducer 2 propagates through the measured fluid and is then received by the ultrasonic receiving transducer 6 after a lapse of time t. This received signal is compared with a reference signal by the comparator 9. When the relationship in voltage between the received signal and the reference signal is inverted, a stop signal is transmitted to the timer 4. In response to this stop signal, the timer 4 stops. The flow velocity v of the measured fluid is calculated by assigning an output value, obtained for time t, in expression (1):
xe2x80x83V=(L/(txe2x88x92a))xe2x88x92cxe2x80x83xe2x80x83(1)
where L denotes the effective distance along a flowing direction between the ultrasonic wave transmitter and the ultrasonic wave receiver, c denotes a sonic velocity, v denotes a flow velocity of the measured fluid, a denotes a delay time from when the signal is received to when the output of the comparator 9 is inverted. A direction from the ultrasonic transducer to the ultrasonic receiving transducer is referred to as the positive direction.
Alternatively, the ultrasonic transducer 2 and the ultrasonic receiving transducer 6 are switched, and a propagation time t1 from upstream to downstream and a propagation time t2 from downstream to upstream are measured so as to obtain a flow velocity v based on expression (2):
v=L/2(1/t1xe2x88x921/t2)+axe2x80x83xe2x80x83(2)
According to this method, the velocity of a flowing fluid can be measured independent from influences caused by a change in sonic velocity due to changes in temperature. Thus, this method has been widely used in measurement of flow velocity, flow rate, distance, etc.
Not only flow velocity/flow rate measurement apparatuses which utilize ultrasonic waves but also general flow velocity/flow rate measurement apparatuses that use many sensors, such as a flow rate sensor, a resistance sensor, a temperature sensor, a voltage sensor, etc. These sensors, which transmit electric signals, are influenced by external conditions such that the sensitivity thereof is changed in some cases. Thus, a flow rate measurement apparatus used in a meter for fuel gas or the like is required to measure even a very small change in flow rate, e.g., 3 liters/hour. In order to correctly detect such a very small change, a measurement apparatus must be structured such that it can perform zero-point correction for measurements.
In view of the above, a technique disclosed in Japanese Laid-Open Publication No. 8-271307 is a gas flow-rate meter which determines, at a predetermined time interval, whether or not performing zero-point correction is appropriate and performs zero-point correction based on such a determination. This is regarded as a very useful technique in the field of gas equipment.
However, when the above conventional structure is applied to a flow rate measurement apparatus for fuel gas such as propane gas, the flow rate of fluid widely varies in a flow path; for example, change in flow rate is very small in some cases, but change in flow rate is several ten-thousand liters per hour in other cases. Accordingly, the input waveform of a received signal widely varies according to the flow velocity. Thus, it is difficult to measure the flow rate without adjusting reception sensitivity.
In general, a sensor which transmits an electric signal is influenced by external conditions such that the sensitivity thereof may be changed. Thus, a flow rate measurement apparatus used in a meter for fuel gas or the like is required to measure even a very small change in flow rate, e.g., 3 liters/hour. In order to correctly detect various magnitudes of change over such a wide range of a very small change to several ten-thousand liters per hour, a measurement apparatus must be structured such that reception conditions for measurement (gain or the like) are adjusted at a predetermined time interval. In such a case, in equipment where a flow of fluid is never interrupted, it is impossible to close a flow path, such that a correction cannot be performed.
In view of the problems involved in the above conventional example, an objective of the present invention is to provide a structure having a plurality of flow paths, wherein the gain of a circuit which receives and amplifies a signal from a sensor is corrected and adjusted in a flow path in which flow rate measurement is not being performed, and the flow path in which the gains of the sensor and the circuit have been adjusted is opened for use in the flow rate measurement.
According to a method for performing zero-point correction, it is determined at a predetermined time interval whether or not it is necessary to perform zero-point correction, and when necessary, the zero-point correction is performed. Thus, in equipment where a flow of fluid is never interrupted, it is impossible to close a flow path, such that the zero-point correction cannot be performed.
In view of the problems involved in the above conventional example, another objective of the present invention is to provide a structure having a plurality of flow paths wherein the zero-point correction is performed in a flow path in which flow rate measurement is not being performed, and the flow path in which the zero-point correction has been completed is opened for use in the flow rate measurement.
The present invention is very useful when it is applied to a meter for fuel gas such as propane gas or city gas. This is because a flow rate measurement apparatus for fuel gas is required to detect a change in the flow rate, e.g., 3 liters/hour. The present invention is useful in that a correct flow rate can be measured by correcting the gains of various sections, such as a measurement section, a flow rate calculation section, etc., over a wide range from a very small flow rate change to several ten-thousand liters per hour.
In view of the above spirit of the present invention, the present invention is useful in any field in which correct measurement of flow rate is required.
A person skilled in the art can practice the present invention by a structure recited in each of the claims. Nevertheless, in addition to means for achieving the claimed inventions and the structures of the claimed inventions, the functions and effects of each of the claims are described so as to help a reader of this specification readily understand the features of the present invention and grasp the embodiments of present invention.
A flow rate measurement apparatus of the present invention includes: a plurality of flow paths provided between an inflow port and an outflow port; opening/closing sections for opening/closing the plurality of flow paths; measurement sections for measuring a flow rate of fluid flowing through at least one of the plurality of flow paths; and a control section for controlling the opening/closing sections and the measurement sections; wherein the control section includes a gain adjustment section for correcting a gain of the measurement section in a flow path which is closed by the opening/closing section. With this structure, the above objective is achieved.
According to the present invention, the flow rate measurement apparatus has a structure including a plurality of flow paths. In such a structure, an extended measurement range of the fluid flow rate can be obtained. Furthermore, even in an apparatus in which flow of fluid does not stop, gain correction is performed in a flow path in which flow rate measurement is not being performed, and then, opening/closing sections are switched so that the flow rate measurement can be performed using the flow path in which the gain correction has been completed. Thus, when this flow path in which the gain correction has been completed is opened, a stable measurement system can be obtained, measurement is free from a variation in reception sensitivity, and the measurement accuracy is prevented from being unstable.
The control section may include a first timer section for switching a flow path so as to be closed by the opening/closing section at a predetermined time interval. With this structure, even when the flow of fluid is maintained and the flow rate thereof is being measured, the gain of a measurement section in a closed flow path is corrected, and opening/closing of flow paths are switched at a predetermined time interval. From such an arrangement, even when a variation in the gain of the measurement section is caused in a flow path in which flow rate measurement is being performed due to a secular change or the like, stable measurement with no variation in reception sensitivity can be recovered within a certain time, and the measurement accuracy is prevented from being unstable.
The control section may include: a flow rate calculation section for calculating a flow rate based on an output of the measurement section; and a flow rate determination section for transmitting to the gain adjustment section a signal which starts a correction of the gain of the measurement section when the flow rate calculated by the flow rate calculation section is lower than a predetermined flow rate. With this structure, in a flow path in which an opening/closing section is closed, a gain point can be corrected when the flow of the fluid is small, and accordingly, an error is not caused due to an external disturbance from downstream.
The control section may include: a flow rate calculation section for calculating a flow rate based on an output of the measurement section; and a flow rate determination section for transmitting to the gain adjustment section a signal which stops a correction of the gain of the measurement section when the flow rate calculated by the flow rate calculation section during the correction of the gain of the measurement section is higher than a predetermined flow rate. With this structure, when the flow rate is increased, gain correction is stopped so that measurement of the flow rate can be immediately started without decreasing the measurement sensitivity. This is because a gain correction operation for a measurement section in a closed flow path can be adversely influenced by an external disturbance caused due to a large quantity of fluid from downstream, or because it, may be required to open the opening/closing sections for allowing the fluid to flow through the flow paths in order to measure a high flow rate.
The control section may include a second timer section for transmitting a signal, which starts a correction of the gain of the measurement section, to the gain adjustment section at a predetermined time interval. With this structure, the gain of a measurement section in a flow path in which an opening/closing section is closed can be corrected at a predetermined time interval. Therefore, even when a variation is caused in the gain due to secular changes including external disturbances, such as temperature, humidity, etc., a correction is performed such that the variation is reduced within a predetermined time.
The control section may include a time measurement section for transmitting a signal, which starts a correction of the gain of the measurement section at a prescribed time, to the gain adjustment section at a predetermined time interval. With this structure, a flow rate state, which is specific to a system in which the flow rate measurement apparatus is installed, is previously measured. For example, a time when the flow rate is low is set in a time measurement section, and the gain correction is performed at the time set in the time measurement section, whereby the accuracy of the measurement section can be adjusted at an optimum time.
The control section may include a time measurement section for storing, in a storage section, a time when a flow rate of fluid flowing through a flow path is continuously maintained equal to or lower than a predetermined flow rate and for transmitting to the gain adjustment section a signal, which starts a correction of the gain of the measurement section, at the time stored in the storage section. With this structure, the use conditions inherent to a system to which the flow rate measurement apparatus is attached and the state of the system are previously stored. Furthermore, the state of the gain of the measurement section is checked at a time when the flow rate is stable, whereby the measurement section can be adjusted more accurately.
The control section may include a communication section for receiving a signal from outside of the flow rate measurement apparatus and transmitting to the gain adjustment section a signal which starts a correction of the gain of the measurement section. With this structure, a user can correct the gain of a measurement section externally at any time. Thus, even when a system becomes unstable due to a sudden external disturbance or the like, a user can manually transmits a signal for correcting the gain.
The measurement section may include: a first transducer and a second transducer which transmit and receive an ultrasonic wave signal; a transmission section for transmitting a periodic drive signal to the first transducer and the second transducer; and a flow rate calculation section for calculating a flow rate based on a propagation time of the ultrasonic wave signal between the first transducer and the second transducer. With this structure, the flow rate can be measured without causing a disturbance in the flow of the fluid. Moreover, due to the available combinations of a plurality of flow paths, the flow rate can be quickly measured with a high accuracy over a wide flow rate range.
The measurement section may include: a thermosensitive section for detecting a change in temperature which is caused by a change in flow rate; and a flow rate calculation section for calculating a flow rate based on an output of the thermosensitive section. With this structure, stable flow rate measurement can be achieved with a control circuit having a simple structure. Furthermore, the measurement section does not have movable parts, and therefore, the failure rate thereof is low. Moreover, due to combinations of a plurality of flow paths, the flow rate can be quickly measured with high accuracy over a wide flow rate range.
A flow rate measurement apparatus of the present invention includes: a plurality of flow paths provided between an inflow port and an outflow port; opening/closing sections for opening/closing the plurality of flow paths; measurement sections for measuring a flow rate of fluid flowing through at least one of the plurality of flow paths; and a control section for controlling the opening/closing sections and the measurement sections; wherein the control section includes a zero-point examination section for detecting and correcting a zero-point of the measurement section in a flow path which is closed by the opening/closing section. With this structure, the above objective is achieved.
According to the present invention, the flow rate measurement apparatus has a structure including a plurality of flow paths. In such a structure, an extended measurement range of the fluid flow rate can be obtained. Furthermore, even in an apparatus in which flow of fluid does not stop, the zero-point correction is performed in a flow path in which flow rate measurement is not being performed, and then, opening/closing sections are switched such that the flow rate measurement can be performed using the flow path in which the zero-point correction has been completed. Thus, when this flow path, in which the zero-point correction has been completed, is opened, a stable measurement system can be obtained, measurement is free from variations in reception sensitivity, and the measurement accuracy is prevented from being unstable.
The control section may include a third timer section for switching a flow path so as to be closed by the opening/closing section at a predetermined time interval. With this structure, even when the flow of fluid is kept and the flow rate thereof is being measured, the zero-point of a measurement section in a closed flow path is corrected, and opening/closing of flow paths are switched at a predetermined time interval. Due to such an arrangement, even when a variation in the zero-point of the measurement section is caused in a flow path in which flow rate measurement is being performed due to a secular change or the like, stable measurement with no variation in reception sensitivity can be obtained within a certain time, and the measurement accuracy is prevented from being unstable.
The control section may include: a flow rate calculation section for calculating a flow rate based on an output of the measurement section; and a flow rate determination section for transmitting to the zero-point examination section a signal which starts a correction of the zero-point of the measurement section when the flow rate calculated by the flow rate calculation section is lower than a predetermined flow rate. With this structure, in a flow path in which an opening/closing section is closed, a zero-point can be corrected when the flow of the fluid is small, and accordingly, an error is not caused due to an external disturbance from downstream.
The control section may include: a flow rate calculation section for calculating a flow rate based on an output of the measurement section; and a flow rate determination section for transmitting to the zero-point examination section a signal which stops a correction of the zero-point of the measurement section when the flow rate calculated by the flow rate calculation section during the correction of the zero-point of the measurement section is higher than a predetermined flow rate. With this structure, when the flow rate is increased, zero-point correction is stopped such that measurement of the flow rate can be immediately started without decreasing the measurement sensitivity. This is because a zero-point correction operation for a measurement section in a closed flow path can be adversely influenced by an external disturbance caused due to a large quantity of fluid from downstream, or because it may be required to open the opening/closing sections for allowing the fluid to flow through the flow paths in order to measure a high flow rate.
The control section may include a fourth timer section for transmitting a signal which starts a correction of the zero-point of the measurement section to the zero-point examination section at a predetermined time interval. With this structure, the zero-point of a measurement section in a flow path in which an opening/closing section is closed can be corrected at a predetermined time interval. Therefore, even when a variation is caused in the zero-point due to secular changes including external disturbances, such as temperature, humidity, etc., a correction is performed such that the variation is reduced within a predetermined time.
The control section may include a time measurement section for transmitting a signal, which starts a correction of the zero-point of the measurement section at a prescribed time, to the zero-point examination section at a predetermined time interval. With this structure, a flow rate state which is specific to a system in which the flow rate measurement apparatus is installed, is previously measured. For example, a time when the flow rate is low is set in a time measurement section, and the zero-point correction is performed at the time set in the time measurement section, whereby the accuracy of the measurement section can be adjusted at an optimum time.
The control section may include a time measurement section for storing in a storage section a time when a flow rate of fluid flowing through a flow path is continuously maintained equal to or lower than a predetermined flow rate and transmitting to the zero-point examination section a signal which starts a correction of the zero-point of the measurement section at the time stored in the storage section. With this structure, the use conditions inherent to a system to which the flow rate measurement apparatus is attached and the state of the system are previously stored, and the state of the zero-point of the measurement section is corrected at a time when the flow rate is stable, whereby the measurement section can be adjusted more accurately.
The control section may include a communication section for receiving a signal from outside of the flow rate measurement apparatus and transmitting to the zero-point examination section a signal which starts a correction of the zero-point of the measurement section. With this structure, a user can externally correct the zero-point of a measurement section at any time. Thus, even when a system becomes unstable due to a sudden external disturbance or the like, a user can manually transmits a signal for correcting the zero-point.
The measurement section may include: a first transducer and a second transducer which transmit and receive an ultrasonic wave signal; a transmission section for transmitting a periodic drive signal to the first transducer and the second transducer; and a flow rate calculation section for calculating a flow rate based on a propagation time of the ultrasonic wave signal between the first transducer and the second transducer. With this structure, the flow rate can be measured without causing a disturbance in the flow of the fluid. Moreover, due to the available combinations of a plurality of flow paths, the flow rate can be quickly measured with high accuracy over a wide flow rate range.
The measurement section may include: a thermosensitive section for detecting a change in temperature which is caused by a change in flow rate; and a flow rate calculation section for calculating a flow rate based on an output of the thermosensitive section. With this structure, stable flow rate measurement can be achieved with a control circuit having a simple structure. Furthermore, the measurement section does not have movable parts, and therefore, the failure rate thereof is low. Moreover, due to combinations of a plurality of flow paths, the flow rate can be quickly measured with high accuracy over a wide flow rate range.
A flow rate measurement apparatus of the present invention includes: a plurality of flow paths provided between an inflow port and an outflow port; opening/closing sections for opening/closing the plurality of flow paths; measurement sections for measuring a flow rate of fluid flowing through at least one of the plurality of flow paths; and a control section for controlling the opening/closing sections and the measurement sections; wherein the control section includes at least one of: a zero-point examination section for detecting and correcting a zero-point of the measurement section in a flow path which is closed by the opening/closing section; a gain adjustment section for correcting a gain of the measurement section in a flow path which is closed by the opening/closing section; and a total flow rate measurement section for measuring a total flow rate of fluid flowing from the inflow port to the outflow port, and the measurement section includes: a first transducer and a second transducer which transmit and receive an ultrasonic wave signal; a transmission section for transmitting a periodic drive signal to the first transducer and the second transducer; an amplifying section for amplifying the received ultrasonic wave signal; a comparison section for comparing a signal output from the amplifying section with a reference signal; a repetition section for repeating ultrasonic wave transmission a plurality of times between the first transducer and the second transducer according to an output of the comparison section; a delay section for delaying the ultrasonic wave transmission during the repetition of the ultrasonic wave transmission; and a flow rate calculation section for calculating a flow rate based on a propagation time of the ultrasonic wave signal between the first transducer and the second transducer. With this structure, the above objective is achieved.